JPS582470B2 - printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel shape of a land portion in a printed wiring board in which solder bridges are less likely to occur.

Conventionally, printed wiring boards were as shown in FIGS. 1 and 2.

FIG. 1 shows a partial plan view of the back surface (printed wiring forming surface) of the printed wiring board 10, and FIG. 2 shows a cross section of section A in FIG.

The printed wiring board 10 has predetermined conductive foils 12, 12... arranged on one surface of an insulating substrate 11, and the conductive foils 12, 12...
A resist 14 is provided to form land portions 13, 13, . . . that require soldering on the surface of the substrate.

Land portions 13, 13... are mounting holes 15, 1 into which lead terminals of mounting components are usually inserted from the surface of the printed wiring board 10.
5..., and the resist 14 is not provided.

Figures 1 and 2 show patterns when the mounting component is an IC, and the shapes of the land portions 13, 13... are also shown for convenience as being different between the left example and the right example. 12 is covered with resist 14, which is indicated by a broken line.

In Fig. 1, the land portions 13, 13... are shown with and without the conductive foil 12 portions indicated by broken lines, but this is also a different example of the land portions 13, 13... shown for convenience. It is.

When an IC is inserted into this and soldered, the result will be as shown in Figures 3 and 4.

FIG. 3 shows the back side of the printed wiring board 10 after soldering,
FIG. 4 shows a cross section of section A in FIG. 3.

The IC 16 connects its lead terminals 17, 17... to the printed wiring board 1.
Insert into the mounting holes 15, 15... from the surface of 0.

Other components to be assembled onto printed wiring board 10 are similarly inserted into their respective mounting holes.

These insertions are performed during the printed wiring board assembly process.

The printed wiring board is then sent to an automatic soldering process.

The automatic soldering process is carried out, for example, by a dipping method, and the printed wiring board 10 is transported by a chain conveyor or the like so that the back surface of the printed wiring board 10 comes into contact with the soldering surface of the solder tank.

The direction of this transfer is the direction of arrow 18 in FIG. 3 (or the opposite direction).

Then, the back surface of the printed wiring board 10 sequentially comes into contact with the solder surface from the front end to the rear end in the direction of arrow 18, and then separates from the solder surface.

When the land portions 13, 13, . . . contact the solder surface, the solder 19, 19, . . . is attached to the land portions 13, 13, .

However, the solders 19, 19... are in a molten state when attached, and have a large specific gravity and surface tension, and the land portion 1
Since the adjacent gaps 20, 20... of 3, 13... are small, solder bridges 21, 21... are formed in the adjacent gaps 20, 20...
occurred often.

These solder bridges 21, 21... connect (short-circuit) the adjacent land parts 13, 13... and have to be removed later, which has disadvantages such as requiring time to inspect and overlooking them. there were.

The present invention has been proposed in view of the above, and is intended to solve the above-mentioned drawbacks by a simple improvement in which the ends of adjacent land portions are made different from each other.

FIG. 5 is a plan view of the back side of a printed wiring board according to an embodiment of the present invention, which corresponds to FIG. 1, and FIG. 6 is a cross-sectional view of the IC in section A in FIG. It is a diagram.

In FIGS. 5 and 6, the same parts as in FIGS. 1 to 4 are designated by the same reference numerals.

What is new in Figures 5 and 6 is the land portions 13, 13...
In the example on the left, the items numbered 1, 3, and 5 from -H, and in the example on the right, the items 2nd and 4th from the top are moved by a predetermined amount in the direction of arrow 18 and in the opposite direction of arrow 18, respectively. This is because the length has been lengthened.

Comparing the long land portion and the short land portion, as shown in FIG. 5, the mounting holes 15, 15, . , 15... to the end 22 of the short land portion is l1, and the length from the mounting holes 15, 15... to the ends 23, 23... of the long land portion is l2, then the relationship l2≒3l1 holds. It is formed.

Therefore, both ends 22 of the short land portion and the long land portion
．． The lengths of 22, 23, and 23 are 2l1 and 2l2, respectively, and the length of both ends 23 and 23 of the long land portion is 2l2.
≒ Length 2l of both ends 22, 22 of the short land portion,
There is a relationship of ×3.

The ends of the opposing land portions of the left example and the right example are designed so that there is a predetermined gap 24, 24, . . . so that they are not connected.

Insert the lead terminal 17 of the IC 16 into the mounting hole 15 from the front surface of the printed wiring board 10 shown in FIG. , the long land portion and the short land portion sequentially contact the solder surface from the direction of arrow 18 and move away from each other.

When the land portions 13, 13... are separated from the solder surface, first the ends 22 of the short land portions in the direction opposite to the arrow 18
is separated from the solder surface, and after a certain period of time, the end 23 of the long land portion in the opposite direction from the arrow 18 is separated.

As described above, according to the present invention, the lengths l1 and l2 of the land portions 13, 13, . (in the direction of arrow 18) and contact the solder liquid surface of the automatic solder tank, the adjacent ends 22 and 23 will separate from the solder liquid surface (cut).
At different times, solder bridges are less likely to occur in the adjacent gaps 20.

The one shown in FIG. 5 is designed so that the printed wiring board 10 can be moved in either the direction of the arrow 18 or the opposite direction. It is sufficient to make the positions of the ends 22 and 23 on the opposite side different from each other.Also, the relationship between l2 and l1 is l2≒2l1
However, it was confirmed through experiments that the effects of the present invention can be expected to be sufficient.

This is affected not only by the length of the land portions 13, 13, .

Furthermore, the shapes of the ends 22 and 23 are not necessarily limited to those of the embodiment, and the ends 22 and 23 are substantially away from the solder liquid surface, and the ends 22 and 23 are
The shape of 23 can be changed in various ways.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the back side of a conventional printed wiring board, Fig. 2 is a sectional view taken along line A-A in Fig. 1, and Fig. 3 is a plan view of the back side of the printed wiring board after soldering. FIG. 4 is a sectional view taken along line A-A in FIG. 3. FIG. 5 is a plan view of the back side of the present invention, which corresponds to FIG.
This figure is a cross-sectional view taken along the line A-A in FIG. 5 after soldering, and corresponds to FIG. 4. 10 is a printed wiring board, 11 is an insulating substrate, 12, 12... is a conductive foil, 13, 13... is a land portion, 14 is a resist, 2
2, 22... and 23, 23... indicate the ends.

Claims (1)

[Claims] 1. Printing in which a plurality of independent conductive foils are arranged adjacent to each other on the surface of an insulating substrate, and land portions with exposed parts requiring soldering on the adjacent surfaces of the conductive foils are arranged in parallel in a predetermined linear direction. 1. A printed wiring board, characterized in that end portions of the adjacent land portions are different from each other in the linear direction.